diff --git a/eemeter/eemeter/models/daily/base_models/c_hdd_tidd.py b/eemeter/eemeter/models/daily/base_models/c_hdd_tidd.py
index 51132ad8..a3256a13 100755
--- a/eemeter/eemeter/models/daily/base_models/c_hdd_tidd.py
+++ b/eemeter/eemeter/models/daily/base_models/c_hdd_tidd.py
@@ -277,11 +277,11 @@ def _c_hdd_tidd_x0(T, obs, alpha, settings, smooth):
     idx_hdd = np.argwhere(T <= c_hdd_bp).flatten()
     idx_cdd = np.argwhere(T >= c_hdd_bp).flatten()
 
-    hdd_beta, _ = linear_fit(obs[idx_hdd], T[idx_hdd], alpha)
+    hdd_beta, _ = linear_fit(T[idx_hdd], obs[idx_hdd], alpha)
     if hdd_beta > 0:
         hdd_beta = 0
 
-    cdd_beta, _ = linear_fit(obs[idx_cdd], T[idx_cdd], alpha)
+    cdd_beta, _ = linear_fit(T[idx_cdd], obs[idx_cdd], alpha)
     if cdd_beta < 0:
         cdd_beta = 0
 
@@ -347,11 +347,11 @@ def bp_obj_fcn(x, grad=[]):
             idx_hdd = np.argwhere(T <= c_hdd_bp).flatten()
             idx_cdd = np.argwhere(T >= c_hdd_bp).flatten()
 
-            hdd_beta, _ = linear_fit(obs[idx_hdd], T[idx_hdd], alpha)
+            hdd_beta, _ = linear_fit(T[idx_hdd], obs[idx_hdd], alpha)
             if hdd_beta > 0:
                 hdd_beta = 0
 
-            cdd_beta, _ = linear_fit(obs[idx_cdd], T[idx_cdd], alpha)
+            cdd_beta, _ = linear_fit(T[idx_cdd], obs[idx_cdd], alpha)
             if cdd_beta < 0:
                 cdd_beta = 0
 
diff --git a/eemeter/eemeter/models/daily/utilities/base_model.py b/eemeter/eemeter/models/daily/utilities/base_model.py
index 24339c67..f63c613e 100755
--- a/eemeter/eemeter/models/daily/utilities/base_model.py
+++ b/eemeter/eemeter/models/daily/utilities/base_model.py
@@ -85,7 +85,7 @@ def linear_fit(x, y, alpha):
         slope = res.slope
         intercept = res.intercept
     else:
-        slope, intercept, _, _ = theilslopes(x, y, alpha=0.95)
+        slope, intercept, _, _ = theilslopes(y, x, alpha=0.95)
 
     return slope, intercept
 
diff --git a/tests/daily_model/utilities/test_base_model.py b/tests/daily_model/utilities/test_base_model.py
index 575f3bb4..48c43825 100644
--- a/tests/daily_model/utilities/test_base_model.py
+++ b/tests/daily_model/utilities/test_base_model.py
@@ -125,7 +125,7 @@ def test_linear_fit():
     y = np.array([2, 4, 6, 8, 10])
     alpha = 0.95
     slope, intercept = linear_fit(x, y, alpha)
-    res = theilslopes(x, y, alpha=0.95)
+    res = theilslopes(y, x, alpha=0.95)
     assert slope == res[0]
     assert intercept == res[1]
 
@@ -137,7 +137,7 @@ def test_linear_fit():
     with pytest.raises(ValueError):
         res = linregress(x, y)
     assert slope == 0
-    assert intercept == 10
+    assert intercept == x[0]
 
 
 def test_get_smooth_coeffs():